1. Field of the Invention
The present invention relates to a new apparatus (image sensor apparatus having an additional display device function) that can be used both as an active-matrix-type display device and as an image sensor.
2. Description of the Related Art
An active-matrix-type display device in which current-control-type light-emitting elements, such as EL (electroluminescence) elements or LEDs (light-emitting diodes), are used is disclosed in, for example, Japanese Unexamined Patent Publication Nos. 8-54836 and 8-129358. Since any of the light-emitting elements used for this type of display device emits light by itself, there are advantages that, unlike liquid-crystal display devices, it does not require a backlight, and dependence upon viewing angle is small. Meanwhile, as facsimile machines are in the midst of becoming more widespread in ordinary households, there has been a demand for more inexpensive ones as household electrical appliances.
However, since image sensors used in conventional facsimile machines require an optical system, a mechanical system, sensors, an illumination system, and the like, which are expensive, it is difficult to achieve lowering of the price of a facsimile machine.
Here, the inventors of the present invention have taken note of the fact that the current-control-type light-emitting element functions also as a PD (photodiode) element depending on the driving conditions and have proposed a new apparatus which can be used both as an active-matrix-type display device and as an image sensor.
In other words, an object of the present invention is to provide an image sensor apparatus having an additional display device function which can be used both as an active-matrix-type display device and as an image sensor by using thin-film optoelectronic transducers which function as light-emitting elements and light-receiving elements.
In order to solve the above-described problems, an image sensor apparatus having an additional display device function of the present invention includes: a plurality of pixels arranged in matrix, scanning lines to which a scanning signal for selecting the pixels in sequence is supplied, and first to third wirings used as signal lines when light emission or light reception is performed by the pixels selected by the scanning line, wherein the pixels includes first pixel section having a first conduction control circuit to which the scanning signal is supplied through the scanning line, and a first thin-film optoelectronic transducer capable of performing light emission and light reception, connected to the first wiring and the second wiring via the first conduction control circuit; and a second pixel section having a second conduction control circuit to which the scanning signal is supplied through the scanning line, and a second thin-film optoelectronic transducer capable of performing light emission and light reception, connected to the first wiring and the third wiring via the second conduction control circuit.
In the image sensor apparatus having an additional display device function of the present invention, since each pixel is formed with first and second thin-film optoelectronic transducers which function as a light-emitting element and a light-receiving element, by only changing the method of driving these thin-film optoelectronic transducers, it is possible to use the image sensor apparatus having an additional display device function as an image sensor apparatus and as a display device. Also, in the image sensor apparatus having an additional display device function of the present invention, since each optoelectronic transducer is formed of a thin-film optoelectronic transducer, it can be manufactured by a semiconductor process in a manner similar to that for an active-matrix substrate of a liquid-crystal display device. Furthermore, since an optical system, a mechanical system, sensors, illumination, and the like, which are expensive, are not required, the readout section and the like of a facsimile machine can be lowered in price.
In the present invention, there is a case in which the conduction control circuit is composed of one thin-film transistor (hereinafter referred to as a TFT) and there is a case in which the conduction control circuit is composed of thin-film transistors of two stages, in each of the first and second pixel sections.
In the case where the conduction control circuit is composed of one TFT, first, the first conduction control circuit and the second conduction control circuit are each formed with one TFT in which the scanning signal is supplied to the gate electrode. Of these TFTs, the TFT of the first conduction control circuit is connected at one of its source and drain regions to the second wiring and connected at the other to the pixel electrode of the first thin-film optoelectronic transducer. Also, the TFT of the second conduction control circuit is connected at one of its source and drain regions to the third wiring and connected at the other to the pixel electrode of the second thin-film optoelectronic transducer.
With such a construction as described above, preferably, a switching circuit is provided such that, when the thin-film optoelectronic transducer is used as a light-emitting element, the wiring of the second and third wirings to which the thin-film optoelectronic transducer is connected is connected to an output circuit for a switch on/off control signal, and when the thin-film optoelectronic transducer is used as a light-receiving element, the wiring of the second and third wirings to which the thin-film optoelectronic transducer is connected is connected to a photocurrent detection circuit, and the first wiring is connected to a constant-voltage power source. With this construction, by only switching the connected state of the second and third wirings by the switching circuit, it is possible to cause both the first and second pixel sections to function as a light-emitting section or a light-receiving section and also possible to cause one of them to function as a light-emitting section and the other to function as a light-receiving section.
In the present invention, when the conduction control circuit is formed of TFTs of two stages, first, the first conduction control circuit and the second conduction control circuit are each formed with a first TFT in which the scanning signal is supplied to the gate electrode and a second TFT in which the gate electrode is connected to the first wiring through the first TFT. Of these TFTs, the second TFT of the first conduction control circuit is connected at one of its source and drain regions to the second wiring and connected at the other to the pixel electrode of the first thin-film optoelectronic transducer. Also, the second TFT of the second conduction control circuit is connected at one of its source and drain regions to the third wiring and connected at the other to the pixel electrode of the second thin-film optoelectronic transducer.
With such a construction as described above, a switching circuit is provided such that, when the thin-film optoelectronic transducer is used as a light-emitting element, the wiring of the second and third wirings to which the thin-film optoelectronic transducer is connected is connected to a constant-voltage power source, and when the thin-film optoelectronic transducer is used as a light-receiving element, the wiring of the second and third wirings to which the thin-film optoelectronic transducer is connected is connected to a photocurrent detection circuit, and the first wiring is connected to an output circuit for receiving a signal for controlling the conduction state of the second TFT. With such a construction, by only switching the connected state of the second and third wirings by the switching circuit, it is possible to cause both the first and second pixel sections to function as a light-emitting section or a light-receiving section, and also possible to cause one of them to function as a light-emitting section and the other to function as a light-receiving section.
In the present invention, the formation area of the pixel electrode of the first thin-film optoelectronic transducer and the formation area of the pixel electrode of the second thin-film optoelectronic transducer are preferably intermingled with each other. With such a construction, when the image sensor apparatus having an additional display device function is used as an image sensor apparatus, the light which is output from the side of the pixel section that functions as a light-emitting section is reflected by a readout object, such as a document, a drawing, or a photograph, and efficiently reaches the side of the pixel section that functions as a light-receiving section.
In the present invention, the formation area of the pixel electrode of the first thin-film optoelectronic transducer and the formation area of the pixel electrode of the second thin-film optoelectronic transducer are preferably such that the center-of-gravity positions of both are close to each other in comparison with a construction in which the outer frame of the pixel electrode is partitioned by a straight line. For example, the formation area of the pixel electrode of the first thin-film optoelectronic transducer is preferably surrounded by the formation area of the pixel electrode of the second thin-film optoelectronic transducer. In this case, the formation area of the pixel electrode of the first thin-film optoelectronic transducer is preferably in the central portion of the formation area of the pixel electrode of the second thin-film optoelectronic transducer. With such a construction as described above, when the image sensor apparatus having an additional display device function is used as an image sensor apparatus, the light which is output from the side of the pixel section that functions as a light-emitting section is reflected by a readout object, such as a document, a drawing, or a photograph, and efficiently reaches the side of the pixel section that functions as a light-receiving section.
In the present invention, a light-shielding layer is preferably formed between the pixel electrode of the first thin-film optoelectronic transducer and the pixel electrode of the second thin-film optoelectronic transducer. With such a construction, even if light is emitted in all directions from the side of the pixel section which functions as a light-emitting section, it is possible for the light-shielding layer to prevent the light from leaking to the portion of the pixel section which functions as a light-receiving section. Therefore, it is possible to read an image from a readout object at a high S/N ratio.